This project has as its objective the investigation of the molecular dynamics of muscular contraction. The primary approach involves the technique of quasi-elastic photon scattering. Coherent laser light is scattered from the system under investigation, i.e., muscle, myosin, actin, etc., and the autocorrelation of fluctuations in the intensity of the scattered light is measured at a point in the scattered field. From the intensity fluctuation autocorrelation it is possible to make statements about the dynamics of the scattering system. So far we have examined various dynamic aspects of myosin, F-actin, acto-HMM, acto-S-1, native thin filaments, native thick filaments, contracting muscle and mobile bacteria.